Sealing device with leakage gas recovery for cyrogenic gas expansion turbine



June 23, 1970 P. DESTIVAL 3,516,756

SEALING DEVICE WITH LEAKAGE GAS RECOVERY FOR CYROGENIC GAS EXPANSIONTURBINE Filed May 15. 1968 V J, l6- J 23 I T5 lza JAL\ l 50 9 7 //V//V7fl) Paw/P5 .955 7/V4L United States Patent U.S. Cl. 415-112 ClaimsABSTRACT OF THE DISCLOSURE Sealing device with leakage gas recovery forcryogenic gas expansion reaction turbine, comprising at least twosealing systems between the chamber of the rotor and a chamber under alower pressure separated by a chamber effecting the recovery of theleakage gas, either the exhaust gas circuit at a temperaturecorresponding to that between the turbine rotor and the bearings of itsshaft, characterized in that the leakage gas recovery chamber isconnected to a point on the circuit of the turbine exhaust gas where thelatter is at a notably higher temperature than the temperatureprevailing in the exhaust chamber, and preferably at a temperature equalto its own.

The present invention concerns a sealing device with leakage gasrecovery for cryogenic gas expansion reaction turbine, comprising atleast two sealing systems between the chamber of the rotor and a chamberunder a lower pressure, separated by a chamber for the recovery of theleakage gas.

Gas reaction expansion turbines, whether they are of the centripetal oraxial type, comprise a sealing device, for example a labyrinth, which isintended to reduce to the minimum the leakage of high-pressure gastowards the low-pressure chambers, either the exhaust chamber or thechamber arranged between the turbine rotor and the bearings of itsshaft. A certain fraction of the highpressure gas neverthelessinfiltrates through the sealing device and becomes mixed with the coldgas at low pressure. Now, the fraction which has thus infiltratedthrough the sealing device has become considerably heated by frictionduring the course of its passage along the rapidly rotating rotor. Itsmixing with the cold expanded gas of the exhaust of the turbine heatsthis to some extent, and therefore reduces the thermodynamic efiiciencyof the expansion effected in the turbine.

These leakages through the sealing device, which are not tooconsiderable in the case of large turbines dealing with high rates ofgas flow, become considerable in relative value in the case of smallhigh-speed turbines which, for example, effect the expansion of hydrogenor helium which have already been cooled to a very low temperature, andin such cases reduce the expansion efficiency very considerably. By wayof example, in the case of a small turbine of 100 m. /h. approximately(brought to normal conditions) for the expansion of helium from 20 barsabsolute to 1.3 bar absolute, effecting the cooling of the helium from20 K. to 13 K., the leakages may reach to of the total flow, and may betaken to temperatures greater by several dozen degrees than that of theexhaust gas, of about 50 to 60 K.; therefore, they considerably heat thelatter.

The present invention has as its object to obviate the aforesaiddisadvantage, to reduce to a very small fraction the leakage rate of thehigh-pressure gas which becomes mixed with the low-pressure gas throughthe sealing device, and to approximate to the theoretical efliciency thethermodynamic efficiency of the cycle through which passes the gassupplied to the expansion turbine.

The sealing device according to the invention is characterised in thatthe leakage gas recovery chamber is connected to a point on the turbineexhaust gas circuit where the gas is at a substantially highertemperature than the temperature prevailing in the exhaust chamber.

It also preferably comprises the following embodiments taken separatelyor in combination:

(a) The leakage gas recovery chamber is connected to a point on theturbine exhaust gas circuit where the gas is at a temperaturesubstantially equal to that prevailing in the recovery chamber;

(b) The chamber under lower pressure is the exhaust chamber of theturbine;

(c) The chamber under lower pressure is the chamber arranged between theturbine rotor and the bearings of its shaft.

The pressure in the recovery chamber being maintained by its connectionwith the exhaust gas circuit near to the exhaust pressure, it will beunderstood that almost all the leakage flow directed towards the exhaustchamber flows by way of the recovery circuit, and that only a very smallfraction becomes mixed with the cold low-pressure gas through the secondsealing system.

As regards the leakage flow towards the chamber arranged between theturbine rotor and the bearings of its shaft, its recovery permitsimproving the thermodynamic efficiency of the overall cycle throughwhich the gas passes, since the entire supply of cold owing to itsheating from its still relatively low temperature to the ambienttemperature would otherwise be lost.

If necessary, although in general this does not in practice seem to benecessary, it is possible to further reduce the flow of gas at highpressure which becomes mixed with the low-pressure gas through thesealing device, by dividing the latter into three separate sealingsystems which are separated by two recovery chambers, or in a moregeneral manner into n separate sealing systems which are separated by(n-l) recovery chambers, each of the recovery chambers being connectedto a point on the exhaust gas circuit at a temperature corresponding tothat of the fraction received in this chamber.

By way of a non-limitative example and with reference to the figureshown in the accompanying drawing, a description will now be given ofthe sealing device according to the invention between the rotor chamberand on the one hand the exhaust chamber and on the other hand thechamber arranged between the rotor and the gas bearings of the shaft, ofa centripetal turbine with a closed rotor for helium expansion.

The expansion turbine is connected to an inlet conduit for the gas underpressure 1, which opens into the annular pressure admission chamber 2.This supplies fixed bladings 3 forming the distributor; on issuingtherefrom, the gas enters the mobile bladings 4 of the turbine rotor 6which rotates in the rotor chamber 5. The turbine rotor, supported bythe shaft 7, comprises an annular exhaust aperture 8 opening into theexhaust chamber 9. The pressure prevailing in the rotor chamber 5 isgreater than the pressures in the exhaust chamber 9 or the chamber 22arranged between the rotor and the bearings of the shaft (not shown).Therefore, it is necessary to provide a sealing device between themobile rotor and the body of the turbine. This device comprises twoportions on either side of the rotor, each divided into two sealingsystems, respectively 12A, 12B and 13A, 13B constituted by labryinths.Between the sealing systems 12A and 12B there is arranged a recoverychamber 14 in which the gas under pressure arrives which has infiltratedalong the rotor and through the sealing system 12A. Conduits 16 and then18 discharge the gas from this chamber towards a point 19 3 on theexhaust gas circuit where the said gas is substantially at the sametemperature.

Arranged between the sealing systems 13A and 13B is a second recoverychamber 15 into which arrives the gas under pressure which hasinfiltrated along the rotor and through the sealing system 13A. Conduits17 and then 18 effect the discharge of the gas from this chamber towardsthe point 19 on the exhaust circuit which is at the same temperature. Itwill be noted that if the leakage gas arriving at the chamber 15 were ata temperature different from the leakage gas arriving at the chamber 14,it could be directed by a different conduit towards another point on thecircuit of the exhaust gas.

The exhaust gas of the turbine is partly heated by a device formaintaining a low temperature, represented diagrammatically by a heatexchanger 20, in countercurrent with a warmer fluid, and then heatedagain in the exchanger 21 in counter-current with the gas underpressure. Then, after addition of leakage gas from the conduit 18 at 19,it is heated to the ambient temperature and re-cycled to the intake sideof the compressor (not shown) which again brings it to the admissionpressure for the turbine, and then re-cycled by the conduit 23 and theexchanger 21 to the conduit 1 for supplying the turbine.

It will be understood that various modifications may be made in thesealing device which has just been described without departing from theframework of the invention.

In particular, the expansion turbine may be axial and not centripetal;it may comprise several stages instead of only one. The heating circuitfor the exhaust gas may be different. The circuit gas may be different,for example air, nitrogen or neon.

What I claim is:

1. In a closed cycle cryogenic gas expansion-compression cycle in whichcompressed gas flowing in a closed circuit enters an expansion reactionturbine comprising a rotor in a rotor chamber and is expanded thereinand is discharged to a chamber under lower pressure than the pressure inthe rotor chamber at a lower temperature than the temperature in therotor chamber and is recompressed and recirculated to the turbine andenters the turbine at a temperature and pressure substantially higherthan the temperature and pressure in the discharge chamber; theimprovement comprising at least two sealing systems between the rotorchamber and a chamber under lower pressure than the rotor chamber, saidat least two sealing systems being separated by a recovery chamber, andconduit means for conveying gas from said recovery chamber to a point insaid closed circuit where the temperature is at a substantially highertemperature than the temperature in said discharge chamher.

2. Apparatus as claimed in claim 1, said chamber under lower pressurebeing said discharge chamber.

3. Apparatus as claimed in claim 1, said turbine rotor having a shaftsupported by bearings, said chamber under lower pressure being disposedbetween the turbine rotor and said bearings.

4. In a method for improving the efficiency of a cryogenic gas expansionreaction turbine in which gas circulates in a closed circuit through theturbine in which it is expanded and cooled and is subsequently warmedand recompressed and reintroduced into the turbine, the turbine having arotor disposed in a rotor chamber and discharging gas to an exhaustchamber, the leakage of gas from the rotor chamber being impeded by atleast two sealing systems arranged serially in the path of gas leakage;the improvement comprising withdrawing gas leakage from between a pairof said at least two sealing systems and reintroducing said withdrawngas into said closed circuit at a point in said circuit where thetemperature of the gas is substantially higher than the temperatureprevailing in the exhaust chamber.

5. A method as claimed in claim 4, the temperature in said closedcircuit at said point of reintroduction being substantially the same asthe temperature of the withdrawn gas.

References Cited UNITED STATES PATENTS 1,037,647 9/ 19 12 London.2,851,289 9/1958 Pedersen. 2,910,328 10/ 1959 Frolich. 3,087,434 4/ 1963Reichenbacher. 3,105,631 10/1963 Hanny. 3,420,434 1/ 1969 Swearingen.

EVERETTE A. POWELL, 1a., Primary Examiner

